The problems of corrosion and scale formation and attendant effects have troubled water systems for years. For instance, scale tends to accumulate on internal walls of various water systems, such as cooling systems, and thereby materially lessens the operational efficiency of the system.
Deposits in lines, heat exchange equipment, etc., may originate from several causes. For example, precipitation of calcium carbonate, calcium sulfate and calcium phosphate in the water system leads to an accumulation of these scale imparting compounds along or around the metal surfaces which contact the flowing water circulating through the system. In this manner, heat transfer functions of the particular system are severely impeded.
Corrosion, on the other hand, is a degradative electrochemical reaction of a metal with its environment. Simply stated, it is the reversion of refined metals to their natural state. For example, iron ore is iron oxide. Iron oxide is refined into steel. When the steel corrodes, it forms iron oxide which, if unattended, may result in failure or destruction of the metal, causing the particular water system to be shut down until the necessary repairs can be made.
Typically, in cooling water systems, the formation of calcium sulfate, calcium phosphate and calcium carbonate, among others, has proven deleterious to the overall efficiency of the cooling water system. Recently, due to the popularity of cooling treatments using high levels of orthophosphate to promote passivation of the metal surfaces in contact with the system water, it has become critically important to control calcium phosphate crystallization so that relatively high levels of orthophosphate may be maintained in the system to achieve the desired passivation without resulting in fouling or impeded heat transfer functions which would normally be caused by calcium phosphate deposition.
Internal treatment, i.e., treatment of the water fed to the system, is necessary to prevent, reduce and/or retard formation of the scale imparting compounds and their resultant deposition. The carbonates of magnesium and calcium are not the only problem compounds as regards scale but also waters having high contents of phosphate and sulfate ions either occurring naturally or added for other purposes cause problems since calcium and magnesium, and any iron or copper present, react with each and deposit as scale. As is obvious, the deposition of scale on the structural parts of a cooling water system causes poorer circulation and lower heat transfer capacity, resulting accordingly in an overall loss in efficiency.
Many conventional scale and corrosion inhibitors exhibit acceptable utility at temperatures up to about 120.degree. F. heat transfer surface temperature. However, beyond that temperature their effectiveness deteriorates. This operating temperature limitation and other problems have been overcome by the present invention.